We continue to use the isolated rat liver perfused for 24 hrs with a suspension of bovine red cells in Krebs-Ringer bicarbonate buffer, containing 3 mu percent bovine serum albumin, as a model system for evaluating factors regulating biosynthesis of twelve specific plasma proteins. In particular, studies are being aimed at a clearer definition of the role of known hormones in modulating enhanced synthesis of the acute phase proteins:fibrinogen, alpha1-acidglycoprotein (Darcy), alpha1-acidglycoprotein (Kawasaki), alpha2 (Acute phase) globulin, haptoglobin, C3 component of complement, hemopexin, and ceruloplasmin. In addition, synthesis of albumin, alpha2 U-globulin, alpha1-macroglobulin will be measured in the same experiments. Interpretation of the mechanism of action of the hormones will be sought with the aid of inhibitors of protein synthesis (cycloheximide), of RNA synthesis (actinomycin D, alpha-amanitin), of glycoprotein synthesis (tunicamycin).